High-resistance memory devices

ABSTRACT

Cross bar array devices and methods of forming the same include first electrodes arranged adjacent to each other and extending in a first direction. Second electrodes are arranged transversely to the first electrodes. An electrolyte layer is disposed between the first electrodes and the second electrodes, the electrolyte layer comprising a nitridated dielectric material.

BACKGROUND Technical Field

The present invention generally relates to cross bar array networks, andmore particularly to cross bar array devices and methods for fabricatingthese devices using electrodes to provide a reduced or scaled contactsize while providing low contact resistance.

Description of the Related Art

Resistive random access memory (RRAM) is considered a promisingtechnology for electronic synapse devices or memristors for neuromorphiccomputing as well as high-density and high-speed non-volatile memoryapplications. In neuromorphic computing applications, a resistive memorydevice can be employed as a connection (synapse) between a pre-neuronand post-neuron, representing the connection weight in the form ofdevice resistance. Multiple pre-neurons and post-neurons can beconnected through a crossbar array of RRAMs, which can express afully-connected neural network configuration.

SUMMARY

Cross bar array devices and methods of forming the same include firstelectrodes arranged adjacent to each other and extending in a firstdirection. Second electrodes are arranged transversely to the firstelectrodes. An electrolyte layer is disposed between the firstelectrodes and the second electrodes, the electrolyte layer comprising anitridated dielectric material.

A cross bar array device includes first electrodes arranged adjacent toeach other and extending in a first direction. Second electrodes arearranged transversely to the first electrodes. An electrolyte is formedon the second electrodes and in contact with the first electrodes suchthat at intersection points between the first and second electrodes aresistive element is formed through the electrolyte, the electrolytelayer comprising a nitridated dielectric material.

A method for forming a cross bar array device includes patterning firstelectrodes arranged adjacent to each other and extending in a firstdirection. An electrolyte is formed over the first electrodes. Theelectrolyte includes a dielectric material. The dielectric material ofthe electrolyte is nitridated to cause nitrogen doping in theelectrolyte. Second electrodes are formed in contact the electrolyte,transversely to the first electrodes.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 is a schematic view of a neuromorphic device architecture withcells or nodes for conducting analog computer operations in accordancewith aspects of the present invention;

FIG. 2 is a schematic diagram of an array of resistive elementscross-connected to row and column conductors and showing a sample outputfor the neuromorphic device architecture in accordance with aspects ofthe present invention;

FIG. 3 is a perspective view of a crossbar array in accordance withaspects of the present invention;

FIG. 4 is a magnified perspective view of the crossbar array of FIG. 3in accordance with aspects of the present invention;

FIG. 5 is a block/flow diagram showing a system/method for implementinga crossbar array in accordance with aspects of the present invention;

FIG. 6 is a cross-sectional view of a crossbar array device having amain electrode material and a second electrode material formed on asubstrate in accordance with aspects of the present invention;

FIG. 7 is a cross-sectional view of the crossbar array device of FIG. 6having the main electrode material and the second electrode materialpatterned to form conductor lines in accordance with aspects of thepresent invention;

FIG. 8 is a cross-sectional view of the crossbar array device of FIG. 7having a dielectric layer formed over the conductor lines in accordancewith aspects of the present invention;

FIG. 9 is a cross-sectional view of the crossbar array device of FIG. 8having a top surface planarized in accordance with aspects of thepresent invention;

FIG. 10 is a cross-sectional view of the crossbar array device of FIG. 9showing an electrolyte, second electrode material and main electrodematerial formed in accordance with aspects of the present invention;

FIG. 11 is a cross-sectional view of the crossbar array device of FIG.10 rotated 90 degrees and showing the electrolyte, second electrodematerial and main electrode material forming conductive lines inaccordance with aspects of the present invention;

FIG. 12 is a cross-sectional view of the crossbar array device of FIG.11 showing a dielectric layer formed over the device in accordance withaspects of the present invention; and

FIG. 13 is a block/flow diagram of a method of forming a crossbar arraydevice in accordance with aspects of the present invention.

DETAILED DESCRIPTION

In accordance with aspects of the present invention, resistive randomaccess memory (RRAM) devices are provided. The RRAMs can be employed forelectronic synapse devices or memristors for neuromorphic computing aswell as high-density and high-speed non-volatile memory applications. Inneuromorphic computing applications, a resistive memory device can beemployed as a connection (synapse) between a pre-neuron and post-neuron,representing a connection weight in the form of device resistance.Multiple pre-neurons and post-neurons can be connected through acrossbar array of RRAMs, which can be configured as a fully-connectedneural network.

Large scale integration of large RRAM arrays with complementary metaloxide semiconductor (CMOS) circuits can enable scaling of RRAM devicesdown to 10 nm and beyond for neuromorphic computing as well ashigh-density and high-speed non-volatile memory applications.

The crossbar array structure may include an undercut or scaled electrodewith a partial undercut that enables the coexistence of high electrodeconductivity and a small active area. This maintains the electrode crosssection area as large as possible to maximize the conductivity and makesthe contact area small to miniaturize the active device area. However,each cross-point should have high resistivity. If the cross-pointresistance is low, then the voltage drop across the metal lines of thearray structure becomes significant, leading decreased predictability inthe current signals through the array. The present embodiments usenitrogen doping of the cross-point structures to increase resistivity.While the present embodiments are described with particular focus on thecross-bar array RRAM structure, the principles of increasing theresistance of the RRAM may also be applied to vertical RRAM structures.

It is to be understood that the present invention will be described interms of a given illustrative architecture; however, otherarchitectures, structures, substrate materials and process features andsteps can be varied within the scope of the present invention.

It will also be understood that when an element such as a layer, regionor substrate is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements can also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements can be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

The present embodiments can include a design for an integrated circuitchip, which can be created in a graphical computer programming language,and stored in a computer storage medium (such as a disk, tape, physicalhard drive, or virtual hard drive such as in a storage access network).If the designer does not fabricate chips or the photolithographic masksused to fabricate chips, the designer can transmit the resulting designby physical means (e.g., by providing a copy of the storage mediumstoring the design) or electronically (e.g., through the Internet) tosuch entities, directly or indirectly. The stored design is thenconverted into the appropriate format (e.g., GDSII) for the fabricationof photolithographic masks, which typically include multiple copies ofthe chip design in question that are to be formed on a wafer. Thephotolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

Methods as described herein can be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case, the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case, the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

It should also be understood that material compounds will be describedin terms of listed elements, e.g., SiGe. These compounds includedifferent proportions of the elements within the compound, e.g., SiGeincludes Si_(x)Ge_(1-x) where x is less than or equal to 1, etc. Inaddition, other elements can be included in the compound and stillfunction in accordance with the present invention. The compounds withadditional elements will be referred to herein as alloys.

Reference in the specification to “one embodiment” or “an embodiment” ofthe present invention, as well as other variations thereof, means that aparticular feature, structure, characteristic, and so forth described inconnection with the embodiment is included in at least one embodiment ofthe present invention. Thus, the appearances of the phrase “in oneembodiment” or “in an embodiment”, as well any other variations,appearing in various places throughout the specification are notnecessarily all referring to the same embodiment.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This can be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises,” “comprising,” “includes” and/or “including,” when usedherein, specify the presence of stated features, integers, steps,operations, elements and/or components, but do not preclude the presenceor addition of one or more other features, integers, steps, operations,elements, components and/or groups thereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like, can be used herein for ease of description todescribe one element's or feature's relationship to another element(s)or feature(s) as illustrated in the FIGS. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the FIGS. For example, if the device in theFIGS. is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the term “below” can encompass both an orientation ofabove and below. The device can be otherwise oriented (rotated 90degrees or at other orientations), and the spatially relativedescriptors used herein can be interpreted accordingly. In addition, itwill also be understood that when a layer is referred to as being“between” two layers, it can be the only layer between the two layers,or one or more intervening layers can also be present.

It will be understood that, although the terms first, second, etc. canbe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another element. Thus, a first element discussed belowcould be termed a second element without departing from the scope of thepresent concept.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIG. 1, a processing device 10 isshown in accordance with one implementation of the present invention.The device 10 employs very-large-scale integration (VLSI) systemsincluding electronic analog circuits. In one embodiment, the device 10includes a neuromorphic processor or neural network to mimicneuro-biological architectures present in the nervous system. The device10 can describe analog, digital, and/or mixed-mode analog/digital VLSIand software systems that implement models of neural systems. Theimplementation of the device 10 can be realized using an array 18 ofcells or nodes 16. The cells or nodes 16 can include, e.g., resistiverandom access memory (RRAM) devices or oxide-based memristors, etc.

The device 10 includes inputs 12 (e.g., x₁, x₂, x₃, . . . ). Inputs 12can include a first electrical characteristic, such as a voltage. Theneuromorphic device 10 includes a set of outputs 14 (e.g., currents: y₁,y₂, y₃, y₄, . . . ).

Referring to FIG. 2, the array 18 of FIG. 1 is shown in greater detail.The array 18 includes conductors 20 and conductors 22 runningtransversely to each other. The conductors 20 and 22 do not connectdirectly at intersection points as the conductors 20 and 22 are disposedon different levels. Instead, the conductors 20 and 22 are connectedthrough resistive cross-point devices 24 located at each node 16.

Resistive cross-point devices 24 provide a highly parallel and scalablearchitecture composed of resistive devices for back-propagating neuralnetworks. The Devices 24 can include resistive random access memory(ReRAM or RRAM) as will be described.

The cross-point devices 24 are configured to alter input signals andstore data information. The cross-point devices 24 can be configured toimplement algorithms or other functions. In other applications, fast andscalable architectures for matrix operations (e.g., inversion,multiplications, etc.) with cross-point devices 24 can be achieved. Inone example, for forward matrix multiplication, voltages (V₁, V₂, V₃,etc.) are supplied on conductors 22 in rows, and currents (I₁, I₂, I₃,I₄, etc.) are read from conductors 20 in columns. Conductance values σare stored as weights. The conductance values in the array 18 includeσ₁₁, σ₁₂, σ₁₃, σ₂₁, σ₂₂, σ₂₃, σ₃₁, σ₃₂, σ₃₃, σ₄₁, σ₄₂, σ₄₃, etc. In oneexample, I₄=V₁σ₄₁+V₂σ₄₂+V₃σ₄₃.

For backward matrix multiplication, the voltages are supplied on thecolumns (20) and current is read from the rows (22). In one embodiment,weight updates can be achieved when voltages are applied on the rows andcolumns at the same time. The conductance values are updated all inparallel. It should be understood that the function and position of rowsand columns are interchangeable, and the columns and rows can beswitched. In some embodiments, pre or post neurons are connected to rowsand columns to provide pre or post processing functions to operationsperformed by the array.

Referring to FIG. 3, an illustrative cross-bar array 50 is shown inaccordance with one embodiment. The crossbar array 50 includes rows 22and columns 20 of conductive lines. The conductive lines 20 include atop electrode 38, a reactive electrode 36 and an electrolyte 34. Theconductive lines 22 include a bottom electrode 30 and an inert electrode32 formed on the bottom electrode 30. Although this particularembodiment describes element 32 as the inert electrode and element 36 asthe reactive electrode, in other embodiments these functions can bereversed. An intersection of the rows 22 and columns 20 forms aresistive cross-point device 24.

In one embodiment, the electrolyte 34 is disposed between the inertelectrode 32 and the reactive electrode 36. The bottom electrode 30 andthe top electrode 38 may be formed from a same conductive material ordifferent conductive materials. The bottom electrode 30 and the topelectrode 38 can include low resistance metals, such as, e.g., Al, W, Cuor other suitable materials.

The inert electrode 32 and the reactive 36 include materials that can beselectively etchable relative to their respective bottom electrode 30and top electrode 38. The reactive and inert electrodes 32 and 36 makecontact with the electrolyte 34. The reactive and inert electrodes 32and 36 are sandwiched between the electrolyte 34 and their respectivemain electrodes (i.e., bottom electrode 30 and top electrode 38).

In one embodiment, the electrolyte 34 includes a metal oxide, such as,e.g., TiO₂, Al₂O₃, HfO₂, MnO₂ or other metal oxides. The electrolyte 34is thin, e.g., about 2 nm to about 10 nm in thickness, to selectivelypermit conduction through when one or both of the main electrodes 30, 38are activated. If the electrolyte 34 includes a metal oxide, the inertelectrode 32 and the reactive electrode 36 are formed from an oxygenscavenging material, such as, TiN. In this way, when an electric fieldis applied at the crossbar device 24, oxygen is drawn into thescavenging material creating a resistive conductive path through theelectrolyte 34. This creates a first resistive state of the cross-pointdevice 24. Another state may include a reset state where a reverse biasor other electric field is applied to at least one of the mainelectrodes 30, 38 to create a second resistive state of the cross-pointdevice 24. In one embodiment, the reverse bias resets the cross-pointdevice 24 to restore its original state.

The voltages applied to one or both of the main electrodes 30, 38 causea break down in the oxide of the electrolyte 34 to adjust the resistancebetween the electrodes 30 and 38 by making the electrolyte 34 moreconductive (or less conductive). The voltages may include millivolts toa few volts (e.g., 3 or 4 volts).

In some embodiments, during operation, a voltage on the top electrode 38can cause a first response in the electrolyte material 34. A voltage onthe bottom electrode 30 can cause a second response in the electrolytematerial 34. Voltages on both the top electrode 38 and the bottomelectrode 30 can provide a third response. The first, second and/orthird responses can include programming a coefficient into theelectrolyte 34 to alter its resistive properties, perform a computationby forming a resistive circuit, reading or writing a coefficient or aresult through the resistive cross-point device 24, etc.

In useful embodiments, the top electrode 38 can include any suitableconductive material or materials. The top electrode 38 can includepolycrystalline or amorphous silicon, germanium, silicon germanium, ametal (e.g., tungsten, titanium, tantalum, ruthenium, zirconium, cobalt,copper, aluminum, lead, platinum, tin, silver, gold), a conductingmetallic compound material (e.g., tantalum nitride, titanium nitride,tungsten silicide, tungsten nitride, ruthenium oxide, cobalt silicide,nickel silicide), carbon nanotube, conductive carbon, graphene, or anysuitable combination of these materials. The conductive material canfurther comprise dopants that are incorporated during or afterdeposition.

The bottom electrode 30 can include any suitable conductive material ormaterials and can include a same or different material than the topelectrode 38. In useful embodiments, the bottom electrode 30 can includepolycrystalline or amorphous silicon, germanium, silicon germanium, ametal (e.g., tungsten, titanium, tantalum, ruthenium, zirconium, cobalt,copper, aluminum, lead, platinum, tin, silver, gold), a conductingmetallic compound material (e.g., tantalum nitride, titanium nitride,tungsten silicide, tungsten nitride, ruthenium oxide, cobalt silicide,nickel silicide), carbon nanotube, conductive carbon, graphene, or anysuitable combination of these materials. The conductive material canfurther comprise dopants that are incorporated during or afterdeposition.

The electrolyte 34 can include a metal oxide although other dielectricelectrolytes may be employed. In useful embodiments, the electrolytelayer 34 includes a material compatible with the scavenging propertiesof one or more of the reactive electrodes 32, 36. The electrolyte layer34 can be deposited by evaporation, atomic layer deposition (ALD),chemical vapor deposition (CVD), sputtering, or another suitabledeposition process. Note that the array 50 is encapsulated in aninterlevel dielectric (not shown).

Referring to FIG. 4 with continued reference to FIG. 3, the resistivecross-point device 24 is shown in greater detail. The resistivecross-point device 24 can be employed for electronic synapse devices ormemristors for neuromorphic computing as well as high-density andhigh-speed non-volatile memory applications. The resistive cross-pointdevice 24 can be employed as a connection (synapse) between a pre-neuronand post-neuron (not shown), representing a connection weight in theform of device resistance. Multiple pre-neurons and post-neurons can beconnected through the crossbar array 50 of RRAMs, which form a neuralnetwork or the like.

Large scale integration of large RRAM arrays, in accordance with aspectsof the present invention, can be employed with CMOS circuits that enablescaling of RRAM devices down to 10 nm and beyond for neuromorphiccomputing as well as high-density and high-speed non-volatile memoryapplications. In one embodiment, a resistance of a high resistance state(HRS) increases as the inverse of the cell area, and a resistance of lowresistance state (LRS) has only a slight dependency on the cell area.The present embodiments take advantage of the increasing HRS/LRSresistance ratio as cell area decreases as a benefit of device scalingby providing the cross bar array structure with miniaturized devices anda highly conductive electrode.

Referring to FIG. 5, an exemplary neuromorphic processing system 100 towhich aspects of the present invention can be applied is shown inaccordance with one embodiment. The processing system 100 includes atleast one computer processing unit (CPU), which includes a neural orprocessing network 104 operatively coupled to other components via asystem bus 105.

The processing network 104 can include one or more neuromorphiccomputing devices including a resistive memory device that can beemployed as a connection (synapse) between one or more pre-neurons andpost-neurons, representing a connection weight in the form of deviceresistance. Multiple pre-neurons and post-neurons can be connectedthrough a crossbar array of RRAMs to form a fully-connected neuralnetwork (104).

A cache 106, a Read Only Memory (ROM) 108, a Random Access Memory (RAM)110, an input/output (I/O) adapter 120, a sound adapter 130, a networkadapter 140, a user interface adapter 150, and a display adapter 160,can be operatively coupled to the system bus 102.

A first storage device 122 and a second storage device 124 areoperatively coupled to system bus 105 by the I/O adapter 120. Thestorage devices 122 and 124 can be any of a disk storage device (e.g., amagnetic or optical disk storage device), a solid state magnetic device,and so forth. The storage devices 122 and 124 can be the same type ofstorage device or different types of storage devices.

A speaker 132 is operatively coupled to system bus 102 by the soundadapter 130. A transceiver 142 is operatively coupled to system bus 102by network adapter 140. A display device 162 is operatively coupled tosystem bus 102 by display adapter 160.

A first user input device 152, a second user input device 154, and athird user input device 156 are operatively coupled to system bus 102 byuser interface adapter 150. The user input devices 152, 154, and 156 canbe any of a keyboard, a mouse, a keypad, an image capture device, amotion sensing device, a microphone, a device incorporating thefunctionality of at least two of the preceding devices, and so forth. Ofcourse, other types of input devices can also be used. The user inputdevices 152, 154, and 156 can be the same type of user input device ordifferent types of user input devices. The user input devices 152, 154,and 156 are used to input and output information to and from system 100.

Of course, the processing system 100 can also include other elements(not shown), as readily contemplated by one of skill in the art, as wellas omit certain elements. For example, various other input devicesand/or output devices can be included in processing system 100,depending upon the particular implementation of the same, as readilyunderstood by one of ordinary skill in the art. For example, varioustypes of wireless and/or wired input and/or output devices can be used.Moreover, additional processors, controllers, memories, and so forth, invarious configurations can also be utilized as readily appreciated byone of ordinary skill in the art. These and other variations of theprocessing system 100 are readily contemplated by one of ordinary skillin the art given the teachings of the present invention provided herein.

The present invention can be a system, a method, and/or a computerprogram product. The computer program product can include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium can be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network can comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention can be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions can execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer can be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection can be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) can execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions can be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionscan also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions can also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams can represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the blocks can occur out of theorder noted in the figures. For example, two blocks shown in successioncan, in fact, be executed substantially concurrently, or the blocks cansometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

Referring to FIG. 6, a cross-sectional view of a partially fabricatedsemiconductor device 52 illustratively shows the formation of a crossbar array in accordance with aspects of the present invention. Thedevice 52 includes a substrate 60, which may be a semiconductor or aninsulator with an active surface semiconductor layer. The substrate maybe crystalline, semi-crystalline, microcrystalline or amorphous. Thesubstrate may be essentially (e.g., except for contaminants) a singleelement (e.g., silicon), primarily (e.g., with doping) of a singleelement, for example, silicon (Si) or germanium (Ge), or the substrate60 may include a compound, for example, Al₂O₃, SiO₂, GaAs, SiC, or SiGe.The substrate 60 may also have multiple material layers, for example, asemiconductor-on-insulator substrate (SeOI), a silicon-on-insulatorsubstrate (SOI), germanium-on-insulator substrate (GeOI), orsilicon-germanium-on-insulator substrate (SGOI). The substrate 60 mayalso have other layers forming the substrate 60, including high-koxides, nitrides, etc. In one or more embodiments, the substrate 60 maybe a silicon wafer or a semiconductor formed on silicon (e.g., InP onGaAs on Si). In various embodiments, the substrate 60 may be a singlecrystal silicon (Si), silicon germanium (SiGe), or III-V semiconductor(e.g., GaAs, InP) wafer, or have a single crystal silicon (Si), silicongermanium (SiGe), or III-V semiconductor (e.g., GaAs) surface/activelayer. In the present embodiment, the substrate 60 will illustrativelybe described as InP, which may be formed on GaAs over Si.

Material for the bottom electrode 30 may be deposited on the substrate60 or layers of the substrate 60. The inert electrode 32 is deposited onthe material for the bottom electrode 30. The bottom electrode 30 andthe inert electrode 32 can be deposited using any suitable depositionprocess, e.g., chemical vapor deposition, atomic layer deposition,sputtering, evaporation, etc.

Referring to FIG. 7, a patterning process is performed to form lines 22by forming a mask and etching the inert electrode 32 and the bottomelectrode 30. In one embodiment, different etching chemistries areemployed to etch the inert electrode 32 and the bottom electrode 30since these materials are selectively etchable relative to each other.The patterning process may include a lithography process or any othersuitable patterning technique. The etching processes can includereactive ion etching (RIE).

Referring to FIG. 8, a dielectric layer 62 is formed over the lines 22to fill in between the lines 22. The dielectric layer 62 will supportthe formation of transverse conductor lines for the cross bar array. Thedielectric layer 62 can include an oxide, such as silicon oxide,although other dielectric materials may be employed.

Referring to FIG. 9, the dielectric layer 62 is planarized (e.g., bychemical mechanical polishing (CMP)). The planarization exposes theinert electrode 32.

Referring to FIG. 10, the electrolyte 34 is formed over the inert andreactive electrodes and the planarized surface. The electrolyte 34 maybe deposited by atomic layer deposition, chemical vapor deposition, orother process to form, e.g., a metal oxide or the like. Next, thereactive electrode 36 is deposited on the electrolyte 34. Then, the topelectrode 38 is formed by deposition on the reactive electrode 36.

In one particular embodiment, the electrolyte 34 may be formed from,e.g., a hafnium oxide or a tantalum oxide. After deposition of theelectrolyte 34, but before deposition of the reactive electrode 36, theelectrolyte 34 may be exposed to a nitridation process such as, e.g., arapid thermal anneal in an ammonia gas at about 500° C. to about 700° C.or plasma nitridation via nitrogen gas or ammonia radicals.Alternatively, the electrolyte 34 may be nitridated in situ duringdeposition using, e.g., an atomic layer deposition or physical vapordeposition process. The resistivity of the ultimate device is controlledby controlling the doping density and depth profiles of the nitrogen inthe electrolyte 34.

In some embodiments, the nitrogen concentration in the electrolyte 34may be between about 1% and about 10% of the atoms in the electrolyte34. In one specific embodiment, with a thermal anneal performed at 600°C. for 40 seconds, the device resistance may be increased by, e.g., 10times while at the same time reducing the variation in resistancebetween individual devices. The nitrogen depth profile depends on thedevice stack—if oxygen vacancies are uniform in the electrolyte 34, auniform nitrogen profile may be used. If oxygen vacancies are created bya reactive layer at one electrode, a higher nitrogen concentration nearthat electrode may be applied.

Oxygen vacancies may result from adding a reactive metal layer on top ofthe electrolyte 34. These vacancies contribute to the formation offilaments. By limiting filament growth, the resistance of the device canbe further increased. The inclusion of nitrogen doping helps inhibitoxygen vacancies and, thus, filament growth.

Referring to FIG. 11, a 90 degree rotated view from the view in FIG. 10is shown to depict trenches formed through the top electrode 38, thereactive electrode 36 and the electrolyte 34. The top electrode 38 andthe reactive electrode 36 can be deposited using any suitable depositionprocess, e.g., chemical vapor deposition, atomic layer deposition,sputtering, evaporation, etc. A patterning process is performed to formlines 20 by forming a mask and etching the top electrode 38 and thereactive electrode 36. In one embodiment, different etching chemistriesare employed to etch the reactive electrode 36 and the top electrode 38since these materials are selectively etchable relative to each other.The patterning process may include a lithography process or any othersuitable patterning technique. The etching processes includes reactiveion etching (RIE).

Referring to FIG. 12, dielectric material 64 is formed to encapsulateand insulate the lines 20 and to form an interlevel dielectric (ILD).Processing can continue with planarization, the formation of additionalcomponents, metallizations, etc.

Referring now to FIG. 13, a method of forming a resistive memory deviceis shown. Block 1302 forms first electrode layer(s) on the substrate. Itis specifically contemplated that the first electrode layers may includethe bottom electrode 30 and the inert electrode 32. Block 1304 etchesthe first electrode layers into first electrodes. Block 1306 then formsdielectric layer 62 by depositing a dielectric fill over and around thefirst electrodes and then planarizing the dielectric fill down to exposethe first electrodes.

Block 1308 deposits the electrolyte layer 34 on the first electrodes. Asnoted above, the electrolyte layer 34 may include a metal oxide such as,e.g., a hafnium oxide or tantalum oxide. Block 1310 then nitridates theelectrolyte layer using, e.g., a rapid thermal anneal in ammonia gas orplasma nitridation. Alternatively, block 1310 may nitridate theelectrolyte 34 in situ while block 1308 deposits the electrolyte layer34.

Block 1312 then deposits the second electrode layer(s) which may includereactive electrode 36 and top electrode 38. Block 1314 patterns thesecond electrode layers to form second electrodes that connect with thefirst electrodes at cross-points through respective sections ofelectrolyte 34.

Having described preferred embodiments for scaled cross bar array withundercut electrode (which are intended to be illustrative and notlimiting), it is noted that modifications and variations can be made bypersons skilled in the art in light of the above teachings. It istherefore to be understood that changes can be made in the particularembodiments disclosed which are within the scope of the invention asoutlined by the appended claims. Having thus described aspects of theinvention, with the details and particularity required by the patentlaws, what is claimed and desired protected by Letters Patent is setforth in the appended claims.

The invention claimed is:
 1. A cross bar array device, comprising: firstelectrodes, arranged adjacent to each other and having a longestdimension that extends in a first direction; second electrodes, having alongest dimension that extends transversely to the longest dimension ofthe first electrodes; an oxygen scavenging layer, disposed between thefirst electrodes and the second electrodes and having a non-square facein contact with the first electrode, with a longest dimension thatextends parallel to the longest dimension of the first electrode,wherein oxygen is drawn into the oxygen scavenging layer when anelectric field is applied; and an electrolyte layer disposed between thefirst electrodes and the second electrodes and having a non-square facefacing the second electrode, with a longest dimension that extendsparallel to the longest dimension of the second electrode, theelectrolyte layer comprising a nitridated dielectric material.
 2. Thedevice as recited in claim 1, wherein the electrolyte layer comprises auniform nitrogen profile.
 3. The device as recited in claim 1, whereinthe electrolyte layer comprises a nitrogen profile having a higherconcentration at a side of the electrolyte layer in contact with areactive metal material.
 4. The device as recited in claim 1, whereinthe nitridated dielectric material comprises an atomic percentage ofnitrogen between about 1% and about 10%.
 5. The device as recited inclaim 1, wherein the electrolyte layer forms a resistive elementprogrammable to provide at least two resistive states.
 6. The device asrecited in claim 1, further comprising a cross-point device formed atintersections of the first and second electrodes.
 7. The device asrecited in claim 6, wherein the cross-point device includes at least tworesistive states based on electric fields generated by the first andsecond electrodes.
 8. The device as recited in claim 1, wherein thenitridated dielectric material comprises one material from the groupconsisting of a nitrogen-doped hafnium oxide and a nitrogen-dopedtantalum oxide.
 9. A cross bar array device, comprising: firstelectrodes, arranged adjacent to each other and having a longestdimension that extends in a first direction; second electrodes, having alongest dimension that extends transversely to the first electrodes; anoxygen scavenging layer, disposed between the first electrodes and thesecond electrodes and having a non-square face in contact with the firstelectrode, with a longest dimension that extends parallel to the longestdimension of the first electrode, wherein oxygen is drawn into theoxygen scavenging layer when an electric field is applied; and anelectrolyte formed on the second electrodes and facing the firstelectrodes, such that a resistive element is formed through theelectrolyte at intersection points between the first and secondelectrodes, and having a non-square face facing the second electrode,with a longest dimension that extends parallel to the second electrode,the electrolyte layer comprising a nitridated dielectric material. 10.The device as recited in claim 9, wherein the electrolyte comprises auniform nitrogen profile.
 11. The device as recited in claim 9, whereinthe electrolyte comprises a nitrogen profile having a higherconcentration at a side of the electrolyte in contact with a reactivemetal material.
 12. The device as recited in claim 9, wherein thenitridated dielectric material comprises an atomic percentage ofnitrogen between about 1% and about 10%.
 13. The device as recited inclaim 9, Wherein the resistive element is programmable to provide atleast two resistive states.
 14. The device as recited in claim 9,wherein the nitridated dielectric material comprises one material fromthe group consisting of a nitrogen-doped hafnium oxide and anitrogen-doped tantalum oxide.
 15. The device as recited in claim 9,further comprising a cross-point device formed at intersections of thefirst and second electrodes, wherein the cross-point device includes atleast two resistive states based on electric fields generated by thefirst and second electrodes.
 16. The device as recited in claim 1,wherein the oxygen scavenging layer is formed from titanium nitride. 17.The device as recited in claim 1, wherein the oxygen scavenging layerand the electrolyte layer are divided into respective strips, with eachoxygen scavenging layer strip contacting multiple electrolyte layerstrips and with each electrolyte layer strip contacting multiple oxygenscavenging layer strips.
 18. The device as recited in claim 1, furthercomprising a second oxygen scavenging layer, positioned between theelectrolyte layer and the second electrode.
 19. A cross bar arraydevice, comprising: a first electrode, having a longest dimension thatextends in a first direction; a first oxygen scavenging layer, having anon-square face in contact with the first electrode, with a longestdimension that extends parallel to the longest dimension of the firstelectrode, wherein oxygen is drawn into the oxygen scavenging layer whenan electric field is applied; an electrolyte layer in contact with thefirst oxygen scavenging layer, with a longest dimension that extendsperpendicular to the longest dimension of the first electrode, theelectrolyte layer comprising a nitridated dielectric material; a secondoxygen scavenging layer, having a non-square face in contact with theelectrolyte layer, with a longest dimension that extends parallel to thelongest dimension of the electrolyte layer; and a second electrode,having a longest dimension that extends parallel to the longestdimension of the electrolyte layer.